Double Trouble: 4 Things to Do in Patients With Diplopia

Brianne N. Hobbs, OD; Erika L. Anderson, OD


November 13, 2019

2. Evaluate the Lids, Pupils, and Extraocular Muscles

When assessing a patient with acute-onset diplopia, it is important to evaluate three ocular structures: the lids, the pupil, and the extraocular muscles.


Diplopia accompanied by unilateral ptosis could be due to a third cranial nerve palsy. Severe ptosis may mask the diplopia caused by the nerve palsy.

Bilateral ptosis with no pupil involvement may be indicative of myasthenia gravis, especially if the ptosis is variable and improves with rest.

Conversely, if the lids seem retracted and lagophthalmos is present, thyroid eye disease should be considered.

Unilateral ptosis with a smaller pupil on the same side may indicate Horner syndrome. The sympathetic fibers travel close to the internal carotid artery, and a carotid artery dissection may present as a painful Horner syndrome. Internal carotid artery dissections may present with diplopia or transient monocular vision loss.


A pupil-involved third cranial nerve palsy is one of the most serious causes of diplopia. The presence of a unilaterally dilated pupil with a third cranial nerve palsy indicates a compressive etiology rather than an ischemic one. Such patients must be referred emergently for neuroimaging and angiography to rule out an aneurysm, with special attention to the posterior communicating artery. A tumor may also compress the superficial pupillary fibers, so neuroimaging is required any time the pupil is involved with diplopia.

Extraocular Muscles

Checking the motility of the extraocular muscles provides important clues to the etiology of the diplopia.

Assessing the cardinal positions of gaze binocularly can reveal muscle restrictions that are the result of trauma or thyroid eye disease, but this test is also useful in establishing whether the deviation is comitant or incomitant. If the alignment of the eyes differs in different positions of gaze (incomitant), then the patient probably will also experience diplopia that varies in magnitude. Incomitant deviations are more characteristic of restrictions or palsies.

Evaluating the cardinal positions of gaze monocularly aids in the detection of subtle abnormalities that may be missed if both eyes are being assessed simultaneously.


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